Semiconductor Device Performance Improvement

ABSTRACT

Embodiment described herein provide a thermal treatment process following a high-pressure anneal process to keep hydrogen at an interface between a channel region and a gate dielectric layer in a field effect transistor while removing hydrogen from the bulk portion of the gate dielectric layer. The thermal treatment process can reduce the amount of threshold voltage shift caused by a high-pressure anneal. The high-pressure anneal and the thermal treatment process may be performed any time after formation of the gate dielectric layer, thus, causing no disruption to the existing process flow.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to United States Provisional PatentApplication Ser. No. 62/565,890, filed on Sep. 29, 2017, which isincorporated herein by reference.

BACKGROUND

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three-dimensional designs, such as a FinField Effect Transistor (FinFET). FinFET devices typically includesemiconductor fins with high aspect ratios and in which channel andsource/drain regions are formed. A gate is formed over and along thesides of the fin structure (e.g., wrapping) utilizing the advantage ofthe increased surface area of the channel to produce faster, morereliable, and better-controlled semiconductor transistor devices.However, with the decreasing in scaling, new challenges are presented.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A-C, 2A-B, 3A-B, 4A-B, 5A-B, 6A-B, 7A-B, and 8A-B are variousviews of respective intermediate structures at intermediate stages in anexample process of forming a semiconductor device in accordance withsome embodiments.

FIG. 9 is a cross-sectional view of a channel region of a transistordevice after a high-pressure anneal process in accordance with someembodiments.

FIG. 10 is a cross-sectional view of the channel region of thetransistor device after a post-anneal treatment process in accordancewith some embodiments.

FIG. 11 includes example hydrogen concentration profiles in devicesformed with and without an example post-anneal treatment process inaccordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. The term “hydrogen” mayinclude hydrogen (H), deuterium (D), and other isotopes of hydrogen.

Methods of forming a semiconductor device, such as including a FinField-Effect Transistor (FinFET), are described herein, along withstructures formed by the methods. Particularly, an embodiment of thepresent disclosure provides a method for improving FinFET performancethrough a high-pressure anneal process and a post-anneal treatmentprocess for threshold voltage recovery.

Example embodiments described herein are described in the context offorming gate structures on FinFETs. Implementations of some aspects ofthe present disclosure may be used in other processes, in other devices,and/or for other layers. For example, other example devices can includeplanar FETs, Horizontal Gate All Around (HGAA) FETs, Vertical Gate AllAround (VGAA) FETs, and other devices. Some variations of the examplemethods and structures are described. A person having ordinary skill inthe art will readily understand other modifications that may be madethat are contemplated within the scope of other embodiments. Althoughmethod embodiments may be described in a particular order, various othermethod embodiments may be performed in any logical order and may includefewer or more steps than what is described herein.

FIGS. 1A-C through 8A-B are views of respective intermediate structuresat intermediate stages in an example process of forming a semiconductordevice in accordance with some embodiments. Particularly, FIGS. 1A-Cthrough 8A-B describe stages of forming FinFET structures with areplacement gate process.

FIGS. 1A, 1B, and 1C illustrate different views of an intermediatestructure at a stage in an example process of forming a semiconductordevice in accordance with some embodiments. FIGS. 1A and 1B aredifferent cross-sectional views of the intermediate structure, and FIG.1C is a perspective view of the intermediate structure.

Fins 74 are on a semiconductor substrate 70. Isolation regions 78 are onthe semiconductor substrate 70 and are disposed between neighboring fins74. The fins 74 each protrude above and from between neighboringisolation regions 78. Gate stacks (or more generically, gatestructures), with each including an interfacial dielectric 80, a dummygate layer 82, and a mask 84, are formed along sidewalls and over topsurfaces of the fins 74. Source/drain regions 52 a-f are disposed inrespective regions of the fins 74.

FIG. 1C further illustrates reference cross-sections that are used inother figures. Cross-section A-A is in a plane along, e.g., channels inone fin 74 between opposing source/drain regions 52 a-c. Cross-sectionB-B is in a plane perpendicular to cross-section A-A and is acrosssource/drain region 52 a and source/drain region 52 d in neighboringfins 74. The figures ending with an “A” designation illustratecross-sectional views at various instances of processing correspondingto cross-section A-A, and the figures ending with a “B” designationillustrate cross-sectional views at various instances of processingcorresponding to cross-section B-B. In some figures, some referencenumbers of components or features illustrated therein may be omitted toavoid obscuring other components or features; this is for ease ofdepicting the figures.

The semiconductor substrate 70 may be or include a bulk semiconductorsubstrate, a semiconductor-on-insulator (SOI) substrate, or the like,which may be doped (e.g., with a p-type or an n-type dopant) or undoped.The semiconductor material of the semiconductor substrate 70 may includean elemental semiconductor including silicon (Si) or germanium (Ge); acompound semiconductor; an alloy semiconductor; or a combinationthereof.

The fins 74 may be formed from the semiconductor substrate 70, such asby etching trenches between the fins 74. The isolation regions 78 may beformed in the trenches between the fins 74. The isolation regions 78 mayinclude or be an insulating material such as an oxide (such as siliconoxide), a nitride, the like, or a combination thereof. The fins 74protrude from between neighboring isolation regions 78, which may, atleast in part, thereby delineate the fins 74 as active areas on thesemiconductor substrate 70. The fins 74 and isolation regions 78 may beformed by any acceptable processes and can include any acceptablematerial. In some examples, the fins 74 may include heteroepitaxialstructures (e.g., a material lattice-mismatched to the semiconductormaterial of the semiconductor substrate 70) or other structures.

The gate stacks are over and extend laterally perpendicularly to thefins 74. The interfacial dielectric 80, dummy gate layer 82, and mask 84for the gate stacks may be formed by sequentially forming respectivelayers, and then patterning those layers into the gate stacks. Theinterfacial dielectric 80 may include or be silicon oxide, siliconnitride, the like, or multilayers thereof. The dummy gates may includeor be silicon (e.g., polysilicon) or another material. The mask 84 mayinclude or be silicon nitride, silicon oxynitride, silicon carbonnitride, the like, or a combination thereof. The layers for theinterfacial dielectrics 80, dummy gate layers 82, and masks 84 maydeposited and then patterned using any acceptable processes to form themask 84, dummy gate layer 82, and interfacial dielectric 80 for eachgate stack.

FIGS. 2A and 2B illustrate the formation of gate spacers 86 along thegate stacks, epitaxy source/drain regions 92 in the fins 74, a contactetch stop layer (CESL) 96 over various components, and a firstinterlayer dielectric (ILD) 100 over the CESL 96. Gate spacers 86 areformed along sidewalls of the gate stacks (e.g., sidewalls of theinterfacial dielectric 80, dummy gate layer 82, and mask 84) and overthe fins 74. Residual gate spacers 86 may remain along sidewalls of thefins 74, for example, depending on the height of the fins 74 above theisolation regions 78. The gate spacers 86 may be formed by conformallydepositing one or more layers for the gate spacers 86 andanisotropically etching the one or more layers, for example. The one ormore layers for the gate spacers 86 may include or be siliconoxycarbide, silicon nitride, silicon oxynitride, silicon carbon nitride,the like, multi-layers thereof, or a combination thereof.

After forming the gate spacers 86, recesses are formed in the fins 74using the gate stacks and gate spacers 86 as masks, and epitaxysource/drain regions 92 are epitaxially grown in the recesses. Therecesses, and hence, the epitaxy source/drain regions 92, are formed inthe fins 74 on opposing sides of the gate stacks. The recessing can beby an etch process, and due to the nature of the etch process, therecesses can have various cross-sectional profiles. The epitaxysource/drain regions 92 may include or be silicon germanium, siliconcarbide, silicon phosphorus, pure or substantially pure germanium, aIII-V compound semiconductor, a II-VI compound semiconductor, or thelike. The epitaxy source/drain regions 92 may extend beyond sidewallsand top surfaces of the fins 74 (e.g., are raised) and may have facets,which may correspond to crystalline planes of the semiconductorsubstrate 70.

A person having ordinary skill in the art will also readily understandthat the recessing and epitaxial growth of source/drain regions 92 maybe omitted, and that source/drain regions may be formed by implantingdopants into the fins 74 using the gate stacks and gate spacers 86 asmasks. In some examples where epitaxy source/drain regions 92 areimplemented, the epitaxy source/drain regions 92 may also be doped, suchas by in-situ doping during epitaxial growth and/or by implantingdopants into the epitaxy source/drain regions 92 after epitaxial growth.Hence, a source/drain region may be delineated by doping (e.g., byimplantation and/or in situ during epitaxial growth, if appropriate)and/or by epitaxial growth, if appropriate, which may further delineatethe active area in which the source/drain region is delineated.

The CESL 96 is conformally deposited on surfaces of the epitaxysource/drain regions 92, sidewalls and top surfaces of the gate spacers86, top surfaces of the mask 84, and top surfaces of the isolationregions 78. Generally, an etch stop layer can provide a mechanism tostop an etch process when forming, e.g., contacts or vias. An etch stoplayer may be formed of a dielectric material having a different etchselectivity from adjacent layers or components. The CESL 96 may compriseor be silicon nitride, silicon carbon nitride, carbon nitride, the like,or a combination thereof. The first ILD 100 is then deposited over theCESL 96. The first ILD 100 may comprise or be silicon dioxide, a low-kdielectric material (e.g., a material having a dielectric constant lowerthan silicon dioxide), such as silicon oxynitride, phosphosilicate glass(PSG), borosilicate glass (BSG), borophosphosilicate glass (BPSG),undoped silicate glass (USG), fluorinated silicate glass (FSG),organosilicate glasses (OSG), SiO_(x)C_(y), Spin-On-Glass,Spin-On-Polymers, silicon carbon material, a compound thereof, acomposite thereof, the like, or a combination thereof.

FIGS. 3A and 3B illustrate the removal of portions of the first ILD 100,portions of the CESL 96 layer, and the mask 84 to expose the dummy gatelayer 82. The first ILD 100 and CESL 96 are formed with top surfacescoplanar with top surfaces of the dummy gate layers 82. A planarizationprocess, such as a CMP, may be performed to level the top surface of thefirst ILD 100 and CESL 96 with the top surfaces of the dummy gate layers82. The CMP may also remove the mask 84 (and, in some instances, upperportions of the gate spacers 86) on the dummy gate layers 82.Accordingly, top surfaces of the dummy gate layers 82 are exposedthrough the first ILD 100 and the CESL 96.

FIGS. 4A and 4B illustrate, after the dummy gate layers 82 have beenexposed through the first ILD 100 and the CESL 96, the removal of thedummy gate layers 82, such as by one or more etch processes. The dummygate layers 82 may be removed by an etch process selective to the dummygate layers 82, wherein the interfacial dielectrics 80 act as etch stoplayers. Recesses 101 are formed between the gate spacers 86.

In some examples, the interfacial dielectrics 80 can be removed by anetch process selective to the interfacial dielectrics 80, and channelregions of the fins 74 are exposed through the recesses 101. Anotherreplacement interfacial dielectric 80 may subsequently be formed in therecesses 101 over the channel regions of the fins 74. In someembodiments, the replacement interfacial dielectric 80 may be a nativeoxide, such as silicon oxide, formed over the fins 74. In someembodiments, the replacement interfacial dielectric 80 may include or besilicon oxide, silicon nitride, the like, or multilayers thereof, andmay be thermally and/or chemically grown on the fins 74, or conformallydeposited, such as by PECVD, ALD, or another deposition technique.

In some examples, the interfacial dielectrics 80 are not removed andremain so that respective replacement gate structures are formed on theinterfacial dielectrics 80, as described subsequently. Subsequentdescription may refer to an interfacial dielectric 80, which may applyto the interfacial dielectrics 80 formed as described with respect toFIGS. 1A-C and/or to the replacement interfacial dielectric 80 describedabove.

FIGS. 5A and 5B illustrate a gate dielectric layer 120 formed in therecesses 101. The gate dielectric layer 120 can be conformally depositedin the recesses 101 where gate stacks were removed (e.g., on topsurfaces of the isolation regions 78, sidewalls and top surfaces of theinterfacial dielectric 80 over the fins 74 along the channel regions,and sidewalls of the gate spacers 86) and on the top surfaces of thefirst ILD 100, the CESL 96, and gate spacers 86. The gate dielectriclayer 120 can be or include silicon oxide (SiO₂), silicon oxynitride(SiON), silicon nitride (SiN), a high-k dielectric material, multilayersthereof, or other dielectric material. A high-k dielectric material mayhave a k value greater than about 7.0. The high-k dielectric materialmay include a metal oxide of or a metal silicate of Hf, Al, Zr, La, Mg,Ba, Ti, Pb, or a combination thereof. The gate dielectric layer 120 canbe deposited by ALD, PECVD, MBD, or another deposition technique. Insome embodiments, the gate dielectric layer 120 may include a high-kdielectric layer formed immediately over the interfacial dielectric 80over the channel regions of the fin 74.

After forming the gate dielectric layer 120, an anneal process and/or apost-anneal treatment process can be performed. The anneal processand/or post-anneal treatment process can be performed immediately afterforming the gate dielectric layer 120 and/or after any processsubsequent to forming the gate dielectric layer 120. Additional detailsof example anneal process and post-anneal treatment process aredescribed further below.

Then, if implemented, one or more conformal layers 121 may beconformally deposited on the gate dielectric layer 120. The one or moreconformal layers 121 can include any combination of one or more barrierlayer, capping layer, and work-function tuning layer. Each implementedconformal layer 121 may be conformally deposited on the gate dielectriclayer 120 or preceding conformal layer 121, where appropriate. Thebarrier layer, capping layer, and work-function tuning layer may eachinclude or be tantalum, tantalum nitride, titanium, titanium nitride,the like, or a combination thereof, and may be deposited by ALD, PECVD,MBD, or another deposition technique.

A conductive fill material 122 is formed over the one or more conformallayers 121, if implemented, or the gate dielectric layer 120. Conductivefill material 122 can fill remaining recesses 101 where the gate stackswere removed. Conductive fill material 122 may be or comprise ametal-containing material such as Co, Ru, Al, W, Cu, multi-layersthereof, or a combination thereof. The conductive fill material 122 canbe deposited by ALD, PECVD, MBD, PVD, or another deposition technique.

Excess conductive fill material 122, one or more conformal layers 121,and gate dielectric layer 120 above the top surfaces of the first ILD100, the CESL 96, and gate spacers 86 are removed by a planarizationprocess, like a CMP. The replacement gate structures each comprising agate dielectric layer 120 and a gate electrode, where the gate electrodeis considered to include the conductive fill material 122 and one ormore conformal layers 121, may therefore be formed as illustrated inFIGS. 6A and 6B.

A second ILD 130 is formed over the first ILD 100, replacement gatestructures, gate spacers 86, and CESL 96. Although not illustrated, insome examples, an etch stop layer (ESL) may be deposited over the firstILD 100, etc., and the second ILD 130 may be deposited over the ESL. Ifimplemented, the etch stop layer may comprise or be silicon nitride,silicon carbon nitride, silicon carbon oxide, carbon nitride, the like,or a combination thereof, and may be deposited by CVD, PECVD, ALD, oranother deposition technique. The second ILD 130 may comprise or besilicon dioxide, a low-k dielectric material, such as siliconoxynitride, PSG, BSG, BPSG, USG, FSG, OSG, SiO_(x)C_(y), Spin-On-Glass,Spin-On-Polymers, silicon carbon material, a compound thereof, acomposite thereof, the like, or a combination thereof. The second ILD130 may be deposited by spin-on, CVD, FCVD, PECVD, PVD, or anotherdeposition technique.

As shown in FIGS. 7A and 7B, conductive features 134 are formed throughthe second ILD 130 and first ILD 100 to the epitaxy source/drain regions92. The conductive features 134 may include an adhesion and/or barrierlayer and conductive material on the adhesion and/or barrier layer, forexample. In some examples, the conductive features 134 may includesilicide regions 136 on the epitaxy source/drain regions 92, asillustrated. The adhesion and/or barrier layer can be conformallydeposited in openings exposing the epitaxy source/drain regions 92 andover the second ILD 130. The adhesion and/or barrier layer may be orcomprise titanium, titanium nitride, titanium oxide, tantalum, tantalumnitride, tantalum oxide, the like, or a combination thereof, and may bedeposited by ALD, CVD, or another deposition technique. Silicide regions136 may be formed on upper portions of the epitaxy source/drain regions92 by reacting upper portions of the epitaxy source/drain regions 92with the adhesion and/or barrier layer. An anneal can be performed tofacilitate the reaction of the epitaxy source/drain regions 92 with theadhesion and/or barrier layer. The conductive material can be depositedon the adhesion and/or barrier layer and fill the openings. Theconductive material may be or comprise tungsten, copper, aluminum, gold,silver, alloys thereof, the like, or a combination thereof, and may bedeposited by CVD, ALD, PVD, or another deposition technique. After thematerial of the conductive features 134 is deposited, excess materialmay be removed by using a planarization process, such as a CMP, forexample, such that top surfaces of the conductive features 134 and thesecond ILD 130 may be coplanar. The conductive features 134 may be ormay be referred to as contacts, plugs, etc.

Additional conductive features are subsequently formed within multipleintermetallization dielectric (IMD) layers to implement electricalconnections for the devices. For example, twelve IMD layers may beformed over transistors in a SRAM device. FIGS. 8A and 8B illustratesubsequent IMDs 140, 142 that are formed over the second ILD 130.Conductive features 144 are formed therein, such as by a damasceneprocess (e.g., dual damascene process), according to the design of thedevice.

According to some embodiments, an anneal process and a post-annealtreatment process are performed to improve the device performance. Insome embodiments, the anneal process and the post-anneal treatmentprocess are performed any time after the formation of the gatedielectric layer 120. The anneal process and the post-anneal treatmentprocess may improve carrier mobility in the device.

In some embodiments, the anneal process is a high-pressure anneal (HPA)process. The high-pressure anneal process may be performed to introduceatoms of small size to passivate dangling bonds at an interface toreduce interface defects. For example, atoms of small size, such ashydrogen or deuterium, can be introduced to the interfacial region(e.g., the interfacial dielectric 80) between the channel region of thefins 74 and the gate dielectric layer 120 to reduce interface defectsand improve carrier mobility in the transistor.

In some embodiments, the high-pressure anneal process is performed in athermal process chamber, such as furnace for processing multiplesubstrates, a single substrate process tool, or other suitable tools. Insome embodiments, the high-pressure anneal process may be performed inan ambient environment of hydrogen (H₂), deuterium (D₂), nitrogen (N₂),argon (Ar), helium (He), or a combination thereof. The high-pressureanneal process may be performed in a pressure in a range from about 5atmosphere to about 70 atmosphere. The process temperature may be in arange from about 200° C. to about 700° C. In some embodiments, theprocess temperature may be in a range from about 350° C. to about 500°C., for example about 400° C. The high-pressure anneal process may beperformed for a time duration in a range from about 3 minutes to about 4hours, for example in a range from about 10 minutes to about 1 hour.

FIG. 9 is a cross-sectional view of a portion of the channel region in afin 74 and the replacement gate structure (e.g., the interfacialdielectric 80 and gate dielectric layer 120) of the transistor deviceafter the high-pressure anneal process in accordance with someembodiments. Hydrogen 150 is introduced to the gate dielectric layer 120and the interfacial dielectric 80 or the interface between the channelregion of the fins 74 and the gate dielectric layer 120.

The channel material in the fins 74 may be or include silicon,germanium, a group IV compound, such as silicon germanium (SiGe), aIII-V compound, another semiconductor material, or a combinationthereof.

The gate dielectric layer 120 can be, for example a high-k dielectriclayer of the FinFET. In some embodiments, the gate dielectric layer 120may include a high-k dielectric material, such as a metal oxide of or ametal silicate of Hf, Al, Zr, La, Mg, Ba, Ti, Pb, or a combinationthereof, silicon oxide (SiO₂), silicon oxynitride (SiON), siliconnitride (SiN), or a combination thereof. In some embodiments, the gatedielectric layer 120 may have a thickness in a range from about 1 nm toabout 10 nm.

The interfacial dielectric 80 may include a native oxide formed over thechannel regions of the fins 74 or a silicon oxide, silicon nitride, orthe like formed by thermal growth, chemical growth, or a conformaldeposition process, such as ALD, CVD, and the like. In some embodiments,the interfacial dielectric 80 may have a thickness in a range fromgreater than 0 nm to about 5.0 nm, such as for example, about 1.0 nm.

Hydrogen atoms in the interfacial dielectric 80 and/or an interfacebetween the channel region of the fin 74 and the gate dielectric layer120 can reduce interface defects and can improve carrier mobility in thetransistor. However, hydrogen atoms in the gate dielectric layer 120 orthe bulk portion of the gate dielectric layer 120 may cause variousproblems, such as shifting of threshold voltage (Vt) of the transistor,particularly in P-type transistors.

Measurements show that after the high-pressure anneal process, hydrogenhas a higher peak concentration at the interfacial dielectric 80 andlower peak concentration at the bulk gate dielectric layer 120. In astructure where the bulk gate dielectric layer 120 has a thickness ofabout 10 nm and the interfacial dielectric 80 has a thickness of 2.5 nm,the total amount of hydrogen atoms in the bulk gate dielectric layer 120is higher than the total amount of hydrogen in the interfacialdielectric 80. In some embodiments, a P-type field-effect transistor hasan initial threshold voltage of about 0.7 volt. Hydrogen introduced inthe high-pressure anneal may cause the threshold voltage to shift byabout 120 mV.

Some embodiments provide a post-anneal treatment process to recover thethreshold voltage shift caused by the high-pressure anneal process. Insome embodiments, the post-anneal treatment process is a rapid thermalprocess, laser anneal process, or the like. The post-anneal treatmentprocess reduces the hydrogen atoms in the bulk gate dielectric layer 120while maintaining the hydrogen concentration in the interfacialdielectric 80.

In some embodiments, the post-anneal treatment process is performed in athermal process chamber, such as furnace for processing multiplesubstrates, a single substrate process tool, or other suitable tools,such as laser anneal tools. In some embodiments, the high-pressureanneal process and post-anneal treatment process may be performed backto back in the same tool.

The post-anneal treatment process may be performed in an ambientenvironment including one or more of nitrogen (N₂), argon (Ar), helium(He), hydrogen (H₂), deuterium (D₂), or a combination thereof. Thecomposition of the ambient environment may be determined by the hydrogenamount in the bulk gate dielectric layer 120 and the interfacialdielectric 80 prior to the process. For example, the ambient environmentmay include nitrogen (N₂), argon (Ar), helium (He), or a combination,but without hydrogen (H₂) or deuterium (D₂) to reduce the hydrogenconcentration in the bulk gate dielectric layer 120. For example, theambient environment includes nitrogen. In another embodiment, theambient environment may include nitrogen (N₂), argon (Ar), helium (He),or a combination and with some hydrogen (H₂) or deuterium (D₂) tomaintain the hydrogen concentration in the interfacial dielectric 80. Insome examples, the composition of an ambient environment may beadjusted, for example by increasing or decreasing the ratio of H₂ or D₂during the process to achieve a target effect, such as to achieve ahydrogen concentration level in the interfacial dielectric 80. In someembodiments, the ratio of H₂ or D₂ in the processing gas to a total ofthe processing gas is in a range from about 0 by flow volume to about100 by flow volume.

In some embodiments, the post-anneal treatment process is performed in arange from about 1 mTorr to about 5 atmosphere. In some embodiments, thepost-anneal treatment process is performed in a low pressure, forexample in a range from 1 Torr to 10 Torr. In some embodiments, thepost-anneal treatment process may be performed in normal atmosphere,such as 1 atmosphere. In some embodiment, the post-anneal treatmentprocess may be performed in a high-pressure, such as in a range from 1atmosphere to 5 atmosphere.

In some embodiments, the process temperature for the post-annealtreatment process is in a range from about 200° C. to about 700° C. Ifthe process temperature is too low, atoms, such as hydrogen atoms, maynot be able to obtain sufficient kinetic energy to move in thedielectric layers. If the process temperature is too high, some layersin the substrate may melt or incur undesired physical or chemicalreactions. In some embodiments, the process temperature may be in arange from about 350° C. to about 500° C., for example about 400° C.

The post-anneal treatment process may be performed for a time durationin a range from about 5 minutes to about 150 minutes. In someembodiments, the post-anneal treatment process is performed for a timeduration in a range from about 10 minutes to about 90 minutes. In someembodiments, the time duration of the post-anneal treatment process canbe sufficiently long to keep hydrogen at an interface between thechannel region and the gate dielectric layer 120 (e.g., in theinterfacial dielectric 80) while removing hydrogen from the bulk portionof the gate dielectric layer 120.

FIG. 10 is a cross-sectional view of the portion of the channel regionand replacement gate structure of the transistor device after thepost-anneal treatment process in accordance with some embodiments.Measurement shows that after the post-anneal treatment process, hydrogenremains at a higher peak concentration at the interfacial dielectric 80and at a lower peak concentration at the bulk gate dielectric layer 120.However, the total amounts of hydrogen atoms in the interfacialdielectric 80 and the bulk gate dielectric layer 120 are substantiallyequal. In some embodiments, the total amount of hydrogen atoms in thebulk gate dielectric layer 120 is lower than the total amount ofhydrogen in the interfacial dielectric 80. The threshold voltage shiftis within a range from about 10 mV to about 20 mV, in some instances. Insome embodiments, the initial threshold voltage before the high pressureanneal process is about 0.7 volt. The final threshold voltage shiftafter the post-anneal treatment process may be in a range from about1.4% to about 2.9% of the initial threshold voltage.

In some embodiments, the anneal process and the post-anneal processreduce peak hydrogen concentration and total hydrogen in the bulk gatedielectric layer 120 and the interfacial dielectric 80. In someembodiments, the anneal process and the post-anneal process increase theratios of peak concentrations and total hydrogen counts in theinterfacial dielectric 80 and in the bulk gate dielectric layer 120. Insome embodiments, after the anneal process and post-anneal process areperformed, the ratio of a peak concentration of hydrogen in theinterfacial dielectric 80 to a peak concentration of hydrogen in thebulk gate dielectric layer 120 is in a range from about 0.1 to about 5,for example about 2.7. In some embodiments, the ratio of a peakconcentration of hydrogen in the interfacial dielectric 80 to a peakconcentration of hydrogen in the bulk gate dielectric layer 120 isgreater than 2.5, such as in a range from greater than 2.5 to about 5.In some embodiments, the ratio of a peak concentration of hydrogen inthe interfacial dielectric 80 to a peak concentration of hydrogen in thebulk gate dielectric layer 120 is greater than or equal to about 2.7,such as in a range from about 2.7 to about 5. In some embodiments, afterthe anneal process and post-anneal process are performed, the ratio oftotal hydrogen counts in the interfacial dielectric 80 and in the bulkgate dielectric layer 120 is in a range from about 0.1 to about 2, forexample about 1.0.

FIG. 11 includes example hydrogen concentration profiles in devices withand without the post-anneal treatment process. The profile 202demonstrates a hydrogen concentration profile in the bulk gatedielectric layer 120 and the interfacial dielectric 80 withoutperforming the anneal process and the post-anneal process describedabove. The profile 204 demonstrates a hydrogen concentration profile inthe bulk gate dielectric layer 120 and the interfacial dielectric 80after performing the anneal process and the post-anneal processdescribed above.

The concentration value PO_(bulk) indicates a peak concentration in thebulk gate dielectric layer 120 in the profile 202. The concentrationvalue PO_(IL) indicates a peak concentration in the interfacialdielectric 80 in the profile 202. The concentration value P_(bulk)indicates a peak concentration in the bulk gate dielectric layer 120 inthe profile 204. The concentration value P_(IL) indicates a peakconcentration in the interfacial dielectric 80 in the profile 204. Inthe example of FIG. 11, when the anneal process and post-anneal processare not performed, the ratio of peak concentrations in the interfacialdielectric 80 and in the bulk gate dielectric layer 120 (PO_(IL):PO_(bulk)) is about 2.5; when the anneal process and post-anneal processare performed, the ratio of peak concentrations in the interfacialdielectric 80 and in the bulk gate dielectric layer 120 (P_(IL):P_(bulk)) is about 2.7. The ratio of peak concentrations in theinterfacial dielectric 80 and in the bulk gate dielectric layer 120increases by about 8.0% when the anneal process and post-anneal processare performed.

In the example shown in FIG. 11, the total hydrogen atoms in the gatedielectric layer 120 and in the interfacial dielectric 80 are about1.13×10⁵ count and about 9.95×10⁴, respectively, when the anneal processand the post-anneal process are not performed. The total hydrogen atomsin the gate dielectric layer 120 and in the interfacial dielectric 80are about 1.04×10⁵ count and about 9.63×10⁴, respectively, when theanneal process and the post-anneal process are performed. In the exampleof FIG. 11, when the anneal process and post-anneal process are notperformed, the ratio of total hydrogen in the interfacial dielectric 80and in the bulk gate dielectric layer 120 is about 0.88, and when theanneal process and post-anneal process are performed, the ratio of totalhydrogen in the interfacial dielectric 80 and in the bulk gatedielectric layer 120 is about 1.0. The ratio of total hydrogen counts inthe interfacial dielectric 80 and in the bulk gate dielectric layer 120increases by about 13.7% when the anneal process and post-anneal processare performed.

The inventors have observed that the increased ratio of total hydrogencounts or peak concentrations in the interfacial dielectric 80 and thebulk gate dielectric layer 120 reduces threshold voltage shift caused bythe high-pressure anneal process.

Referring to FIG. 8A, the bulk gate dielectric layer 120 covers theinterfacial dielectric 80 and sidewalls of the spacers 86. In someembodiments, the hydrogen concentration within the bulk gate dielectriclayer 120 decreases in a direction away from the interfacial dielectric80. Accordingly, the hydrogen concentration in the bulk gate dielectriclayer 120 is higher at the portion near a bottom of the spacer 86 (nearthe epitaxy source/drain regions 92) than at the portion near the secondILD 130.

In some embodiments, the anneal process and the post-anneal treatmentprocess may be performed after conductive features are completed in thetop most IMD, as shown in FIGS. 8A and 8B. In another embodiment, theanneal process and the post-anneal treatment process are performed afterthe formation of the gate dielectric layer 120, as shown in FIGS. 5A and5B, and before forming the one or more conformal layers 121 andconductive fill material 122. In another embodiment, the anneal processand the post-anneal treatment process may be performed after thereplacement gate structures are completed, as shown in FIGS. 6A and 6B.In another embodiment, the anneal process and the post-anneal treatmentprocess may be performed after formation of the conductive features inthe second ILD 130 as shown in FIGS. 7A and 7B. The anneal process andthe post-anneal treatment process may be performed back to back, forexample, performed back to back in the same process chamber. In someexamples, the anneal process and the post-anneal treatment process maybe performed separately at suitable time.

Some embodiments provide a thermal treatment process following ahigh-pressure anneal process to keep hydrogen at interface between achannel region and a gate dielectric layer in a field effect transistorwhile removing hydrogen from the bulk portion of the gate dielectriclayer. The thermal treatment process can reduce the amount of thresholdvoltage shift caused by a high-pressure anneal. The high-pressure annealand the thermal treatment process may be performed at any time afterformation of the gate dielectric layer, thus, causing no disruption ofthe existing process flow.

One embodiment provides a method comprising performing a high pressureanneal process to a structure having a conformal dielectric layer formedover a channel region of an active area to introduce hydrogen to aninterface between the conformal dielectric layer and the channel region,and after performing the high-pressure anneal process, performing apost-anneal treatment to reduce hydrogen in the conformal dielectriclayer.

Another embodiment provides a structure. The structure includes anactive area on a substrate. The active area has a channel region. Thestructure further includes a gate structure over the channel region ofthe active area. The gate structure includes an interfacial layer overthe active area, a conformal dielectric layer over the interfaciallayer, and a gate electrode layer over the interfacial layer. A ratio ofa peak concentration of hydrogen in the interfacial layer to a peakconcentration of hydrogen in the conformal dielectric layer is in arange from about 0.1 to about 5.

Yet another embodiment provides a method comprising forming an activearea on a substrate, wherein the active area has a channel region,forming a dummy gate structure over the channel region of the activearea, removing the dummy gate structure to expose the channel region ofthe active area, forming an interfacial layer over the channel region ofthe active area, forming a conformal dielectric layer over theinterfacial layer, performing a high pressure anneal process tointroduce hydrogen to the interfacial layer, and after performing thehigh-pressure anneal process, performing a post-anneal treatment toreduce hydrogen in the conformal dielectric layer.

Yet another embodiment provides a method comprising forming a gatestructure over a channel region of an active area, wherein the gatestructure includes a conformal dielectric layer over the active area,annealing the gate structure at a first pressure to introduce hydrogento an interface between the conformal dielectric layer and the channelregion, and performing a post-anneal treatment on the gate structure ata second pressure to reduce hydrogen in the conformal dielectric layer,wherein the first pressure is higher than the second pressure.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A structure comprising: an active area on a substrate, the active area having a channel region; a gate structure over the channel region of the active area, wherein the gate structure includes: an interfacial layer over the active area; a conformal dielectric layer over the interfacial layer; and a gate electrode layer over the interfacial layer; and wherein a ratio of a peak concentration of hydrogen in the interfacial layer to a peak concentration of hydrogen in the conformal dielectric layer is in a range from about 0.1 to about
 5. 2. The structure of claim 1, wherein the interfacial layer includes a native oxide, silicon oxide, silicon nitride, silicon oxynitride, or a combination thereof.
 3. The structure of claim 1, wherein the interfacial layer has a thickness in a range from greater than 0 nm to 5 nm.
 4. The structure of claim 1, wherein the conformal dielectric layer includes a high-k dielectric layer, a silicon oxide layer, a silicon oxynitride layer, a silicon nitride layer, or a combination thereof.
 5. The structure of claim 1, wherein the ratio of the peak concentration of hydrogen in the interfacial layer to the peak concentration of hydrogen in the conformal dielectric layer is in a range from about 2.7 to about
 5. 6. The structure of claim 1, wherein a ratio of a total hydrogen count in the interfacial layer to a total hydrogen count in the conformal dielectric layer is in a range from about 0.1 to about
 2. 7. The structure of claim 1, wherein hydrogen concentration in the conformal dielectric layer is higher at a location proximate to the interfacial layer than at a location distal from the interfacial layer.
 8. A method comprising: performing a high-pressure anneal process to a structure having a conformal dielectric layer formed over a channel region of an active area to introduce hydrogen to an interface between the conformal dielectric layer and the channel region; and after performing the high-pressure anneal process, performing a post-anneal treatment to reduce hydrogen in the conformal dielectric layer.
 9. The method of claim 8, wherein performing the post-anneal treatment comprises: exposing the structure to an ambient environment comprising at least one of nitrogen (N₂), argon (Ar), helium (He), hydrogen (H₂), deuterium (D₂), or a combination thereof.
 10. The method of claim 8, wherein performing the post-anneal treatment comprises: exposing the structure to an ambient environment at a temperature in a range from about 200° C. to about 700° C.
 11. The method of claim 8, wherein the post-anneal treatment is performed at a pressure in a range from about 1 mTorr to about 5 atmosphere.
 12. The method of claim 8, wherein the high-pressure anneal process and the post-anneal treatment are performed in the same chamber.
 13. The method of claim 8, wherein the high-pressure anneal process and the post-anneal treatment are performed in different chambers.
 14. The method of claim 8, wherein performing the high-pressure anneal process comprises: exposing the structure to an anneal ambient environment of hydrogen (H₂), deuterium (D₂), nitrogen (N₂), argon (Ar), helium (He), or a combination thereof.
 15. The method of claim 8, wherein: the interface between the conformal dielectric layer and the channel region includes an interfacial layer; and after performing the post-anneal treatment, a ratio of a peak concentration of hydrogen in the interfacial layer to a peak concentration of hydrogen in the conformal dielectric layer is in a range from about 0.1 to about
 5. 16. The method of claim 8, wherein: the interface between the conformal dielectric layer and the channel region includes an interfacial layer; and after performing the post-anneal treatment, a ratio of a total hydrogen count in the interfacial layer to a total hydrogen count in the conformal dielectric layer is in a range from about 0.1 to about
 2. 17. A method, comprising: forming a gate structure over a channel region of an active area, wherein the gate structure includes a conformal dielectric layer over the active area; annealing the gate structure at a first pressure to introduce hydrogen to an interface between the conformal dielectric layer and the channel region; and performing a post-anneal treatment on the gate structure at a second pressure to reduce hydrogen in the conformal dielectric layer, wherein the first pressure is higher than the second pressure.
 18. The method of claim 17, wherein the first pressure is in a range from about 5 atmosphere to about 70 atmosphere, and the second pressure is in a range from about 1 mTorr to about 5 atmosphere.
 19. The method of claim 17, wherein the post-anneal treatment comprises an ambient environment of nitrogen (N₂), argon (Ar), helium (He), hydrogen (H₂), deuterium (D₂), or a combination thereof.
 20. The method of claim 19, wherein the ambient environment is at a temperature in a range from about 350° C. to about 500° C. 